80 GHz Phase Shifter in Liquid Crystal Compact Coplanar Transmission Line with Curved Bends

This work proposes and characterizes a compact coplanar transmission line with 90° curved bends for a liquid crystal-filled coplanar waveguide (CPW) continuously variable phase shifter up to 80 GHz. The device has 90° curved bends for the metalized core line, coplanar grounds, and coplanar channels that are filled with liquid crystals that can be adjusted in dielectric constants. The device with a reduced footprint achieves a differential phase shift of 447.22289° at 80 GHz at the expense of 5.98894 dB insertion loss, i.e., 74.7°/dB in figure-of-merit (FoM). The added curved bend for miniaturization (as compared with the straight line-only design that is longer in size) exhibits a negligible difference in FoM for frequency bands lower than 20 GHz. As the frequency increases, the undesired curved bending effect on phase shift disturbance and insertion loss surge becomes more noticeable, and at 80 GHz, there is a 10°/dB decline in FoM (in comparison to the straight line-only design).